Conventional methods of producing crimped fibers using a stuffer box apparatus are well known, and generally include directing fibers between two driven rollers to force the fibers into a confined space (i.e., the stuffer box chamber). The stuffer box typically includes opposing doctor blades positioned close to a nip, which is formed by the two rollers. Side plates, and occasionally base plates as well, complete the crimping chamber. As the fibers are fed through the nip into the stuffer box chamber, the fibers accumulate, decelerate, and fold. The resulting fiber bends are referred to as "primary" crimps.
To facilitate the formation of primary crimps, a stuffer box is typically equipped with a flapper, which is located toward the back of the crimping chamber. An applied force moves the flapper deep into the crimping chamber, further restricting fiber movement through the stuffer box. This augments the forces exerted on the advancing fibers by the top and bottom doctor blades.
Exemplary stuffer box descriptions are set forth in U.S. Pat. Nos. 5,025,538; 3,353,222; 4,854,021; 5,020,198; 5,485,662; 4,503,593; 4,395,804; and 4,115,908. It will be understood, of course, that these patents provide a descriptive background to the invention rather than any limitation of it. The basic stuffer box design may be modified to include or exclude parts. Although by no means is this list of patents exhaustive, the disclosed patents nevertheless illustrate the basic stuffer box, structural elements.
Conventional crimping methods often fail to manipulate the stuffer box settings to produce fibers having substantially uniform primary and secondary crimps. This can result in fibers that demonstrate relatively poor crimp uniformity, and consequently variable and inconsistent fiber properties. As will be understood by those having quality control backgrounds, use of such inferior fibers in manufacturing certain products is undesirable.
For example, as a general matter, more crimps per unit length increases cohesion and, conversely, fewer crimps per unit length decreases cohesion. Depending on fiber use, cohesion may be advantageous (e.g., carding) or disadvantageous (e.g., fiberfilling). Regardless of the end use, fiber uniformity is beneficial because crimps per unit length may be maintained at a frequency that results in an optimal cohesion, whether high or low. In short, consistent fiber crimping means less deviation from the desired cohesion level. This promotes better quality control.
To the extent that the prior art discloses techniques to improve fiber crimp uniformity, the focus is exclusively upon ways to improve primary crimps. Nevertheless, fibers possessing regular primary crimps can fold into larger deformations as the fibers advance through the stuffer box chamber. These larger fiber deformations are referred to as "secondary crimps." Each secondary crimp fold includes a plurality of primary crimp folds. The formation of secondary crimps depends, in part, upon the gap height between the doctor blades.
Conventional methods which recognize that secondary crimps can form within a common stuffer box apparatus nonetheless fail to teach or suggest regulating the fold dimensions of secondary crimps to provide desirable fiber properties. This is apparent by examining fibers that have emerged from a conventional stuffer box chamber--the step of the folds is usually non-uniform.
The present invention recognizes, however, that primary and secondary crimp uniformity reduces the variability of polyester fiber properties. Such quality control with respect to crimp uniformity improves the manufacturing operations that process polyester fibers. As will be understood by those with quality control experience, reducing manufacturing variability leads to better quality products. Therefore, a need exists for producing crimped fibers having substantially uniform primary and secondary crimps.